Water-absorbing composites, preparation processes thereof and water-absorbing articles

ABSTRACT

A water-absorbing composite, containing water-absorbing polymer particles immobilized on a fibrous substrate wherein at least a part of said water-absorbing polymer particles consist of primary particles having an average particle diameter of about 50-1000 μm, wherein about 30% by weight or more of said primary particles are combined to form agglomerates having a shape satisfying the conditions below while nearly maintaining their primary particle shapes and a part of particles of said agglomerates are not adhered to said fibrous substrate. This water-absorbing composite shows excellent water-absorbing properties and a high water-absorbing speed, and most of the highly water-absorbing polymer is stably immobilized on the fibrous substrate and the immobility of swollen gel after absorbing water is also excellent.  
     Average particle diameter (D) 100≦D≦3000 μm  
     Average relative displacement of the direction by direction analysis (θ) 10≦θ≦25  
     Frequency analysis 5 Hz/20 Hz intensity ratio (k) 0.6≦k≦0.9  
     Agglomerate maximum length (L)/minimum length (l) ratio 1.2≦L/l≦15.0.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to water-absorbing compositescontaining water-absorbing polymer particles in the form of agglomeratesimmobilized on a fibrous substrate and preparation processes thereof.More specifically, the present invention relates to water-absorbingcomposites containing agglomerates of water-absorbing polymer particlesstably immobilized on a fibrous substrate and having goodwater-absorbing properties, a high water-absorbing speed and anexcellent immobility of swollen gel after absorbing water as well aspreparation processes thereof. The present invention also relates towater-absorbing articles using a water-absorbing composite having thesecharacteristics.

[0003] 2. Description of the Background

[0004] Paper, pulp, nonwoven fabric, sponge-like urethane resins or thelike have been used as water-retaining materials in various sanitarygoods such as sanitary napkins, paper diapers and agriculturalmaterials, for example. However, the water-absorbing capacity of thesewater-absorbing materials is only 10-50 times their own weight. Thus,larger amounts of materials are required to absorb or retain largeramounts of water, consequently leading to enormous bulk. These materialsalso have the disadvantage that they readily release water whenpressurized after absorbing water.

[0005] For the purpose of lessening such disadvantages of these types ofmaterials, various highly water-absorbing polymer materials haverecently been proposed, such as starch graft polymers (JP-B 46199/88),modified cellulose (JP-A 80376/75), crosslinked water-soluble polymers(JP-B 23462/68), self-crosslinked acrylic alkali metal salt polymers(JP-B 30710/79), etc.

[0006] These water-absorbing polymers exhibit high level ofwater-absorbing performance, but most are powdery. Accordingly, suchwater-absorbing polymer powders must be uniformly dispersed on asubstrate such as tissue, nonwoven fabric or paper for use as sanitarymaterials such as sanitary napkins or paper diapers. However,water-absorbing polymer powders dispersed by known methods have thefollowing disadvantages. First, they are difficult to stably immobilizeon a fibrous substrate, and even if uniformly dispersed, they oftenbecome locally concentrated. Second, swollen gels after absorbing waterfail to stably remain on a fibrous substrate but readily move from thefibrous substrate.

[0007] When such polymer powders as noted above are uniformly dispersedon a fibrous substrate to give an absorbent, not only are the polymerpowders readily separated from the fibrous substrate, but very high costoccurs due to complexity of powder handling and process design forefficient uniform dispersion.

[0008] Conventional approaches to addressing these problems include, forexample, fixing polymer powder on a fibrous substrate with a binder orcoating an aqueous polyacrylic metal salt solution on a substrate andthen introducing crosslinkage by a heat-drying process. However, theformer suffers from complexity due to the use of the binder and thelatter also has drawbacks, such as insufficient water-absorbingperformance.

[0009] A process for preparing a water-absorbing composite by preparinga composite containing an aqueous acrylic monomer solution applied in apredetermined pattern on a shaped fibrous substrate and irradiating itwith electromagnetic radiations or particulate ionizing radiations toconvert the acrylic monomer into a water-swelling polymer has beenreported (JP-B 67712/91). This process affords an improved powderhandling, such as formation of a uniform dispersion and stableimmobilization on a fibrous substrate as described above, but it has thedisadvantage that the electromagnetic radiation or particulate ionizingradiation used to convert the acrylic monomer into a water-absorbingpolymer markedly accelerates self crosslinking reaction of thewater-absorbing polymer to greatly lessen the performance as awater-absorbing material, especially water-absorbing capacity, i.e.usually to half of that obtained with the highly water-absorbing polymerpowders previously described. In particular, the highly polymerizableaqueous acrylic monomer solution is absorbed into the fibrous substrateitself to form a very hard plate-like composite after polymerization,which must be broken for actual use. Moreover, absorbing capacity,especially water-absorbing capacity is greatly lowered by the inhibitoryeffect of the fibrous substrate against swelling of the water-absorbingpolymer.

[0010] An absorbing article containing a fibrous substrate and awater-absorbing polymer wherein a part of the water-absorbing polymernearly spherically encloses and discontinuously adheres to the substratehas also been proposed (JP-B 58030/93). This absorbing article affordspartially improved water-absorbing characteristics over the above priorproducts, but it has the disadvantages that hydrophilic fibers areunsuitable for the fibrous substrate though this is a water-absorbingarticle, and that the water-absorbing polymer loses adhesion and tendsto be readily separated after becoming swollen with absorbed water.

[0011] Hence, a need exists for a water-absorbing composite whichovercomes the above disadvantages.

SUMMARY OF THE INVENTION

[0012] Quite surprisingly, it has now been discovered that awater-absorbing composite with excellent water-absorbing properties andwater-absorbing speed wherein highly water-absorbing polymer particlesare stably immobilized on a fibrous substrate can be prepared bypolymerizing droplets of a mixed solution of an aqueous polymerizableacrylic monomer solution initialized with a redox polymerizationinitiator on a fibrous substrate (JP-A 67403/97).

[0013] Accordingly, it is an object of the present invention is toprovide a water-absorbing composite with excellent water-absorbingproperties and a high water-absorbing speed wherein most of the highlywater-absorbing polymer is stably immobilized on a fibrous substrate andthe immobility of swollen gel after absorbing water is also excellentand a process for preparing it.

[0014] It is also an object of the present invention to provide awater-absorbing article with high practicability using a water-absorbingcomposite having said properties.

[0015] The above objects and others are provided, in part, by awater-absorbing composite, containing water-absorbing polymer particlesimmobilized on a fibrous substrate wherein at least part of thewater-absorbing polymer particles contain primary particles having anaverage particle diameter of about 50-1,000 μm, wherein about 30% byweight or more of the primary particles are considered to formagglomerates having a shape satisfying the following conditions whilenearly maintaining their primary particle shapes and a part of particlesof the agglomerates are not adhered to the fibrous substrate:

[0016] Average particle diameter (D) 100≦D≦3000 μm

[0017] Average relative displacement of the direction by directionanalysis (θ) 10≦≦25

[0018] Frequency analysis 5 Hz/20 Hz intensity ratio (k) 0.6≦k≦0.9

[0019] Agglomerate maximum length (L)/minimum length (l) ratio1.2≦L/l≦15.0.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a schematic view showing an example of the nozzlestructure used to carry out the mixing step in a process of the presentinvention, in which numeral references represent the following elements.1: nozzles for a first solution, 2: nozzles for a second s solution, 3:solution A, 4: solution B.

[0021]FIGS. 2 and 3 are light microphotographs of water-absorbingcomposite A prepared in Example 1.

[0022]FIG. 4 is a scanning electron microphotograph of water-absorbingcomposite A prepared in Example 1.

[0023]FIG. 5 is a light microphotograph of water-absorbing composite Jprepared in Comparative example 1.

[0024]FIG. 6 is a scanning electron microphotograph of water-absorbingcomposite N prepared in Comparative example 4.

[0025]FIG. 7 is a sectional view showing the structure of thewater-absorbing article prepared in Example 10, in which numeralreferences represent the following elements. 11: nonwoven cloth, 12:paper, 13: fluffy pulp, 14: fibrous substrate, 15: water-absorbingpolymer particles, 16: polyethylene film.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The present invention provides a water-absorbing compositecontaining water-absorbing polymer particles immobilized on a fibroussubstrate wherein at least a part of the water-absorbing polymerparticles contain primary particles having an average particle diameterof about 50-1000 μm, 30% by weight or more of the primary particlesbeing combined to form agglomerates having a shape satisfying theconditions below while nearly maintaining their primary particle shapesand a part of particles of said agglomerates are not adhered to saidfibrous substrate:

[0027] Average particle diameter (D) 100≦D≦3000 μm

[0028] Average particle displacement of the direction by directionanalysis (θ)10≦0≦25

[0029] Frequency analysis 5 Hz/20 Hz intensity ratio (k) 0.6≦k≦0.9

[0030] Agglomerate maximum length (L)/minimum length (l) ratio1.2≦L/1≦15.0.

[0031] The present invention also provides a process for preparing awater-absorbing composite, containing forming droplets of a reactionmixture initialized by mixing an aqueous solution of a polymerizablemonomer giving a water-absorbing polymer with a redox polymerizationinitiator in a gas phase, combining said droplets into agglomerateswhile nearly maintaining their primary particle shapes in the gas phaseand/or on a fibrous substrate, supporting said agglomerates formed inthe gas phase on said fibrous substrate, and then completingpolymerization of said agglomerates on said fibrous substrate toimmobilize said agglomerates on said fibrous substrate.

[0032] The present invention also provides a water-absorbing articlecontaining a water-absorbing material having water-absorbing polymerparticles immobilized on one side of a fibrous substrate so that saidwater-absorbing polymer particles absorb aqueous liquids through saidfibrous substrate, wherein at least a part of said water-absorbingpolymer particles contain primary particles having an average particlediameter of about 50-1000 μm, 30% by weight or more of said primaryparticles are combined to form agglomerates having a shape satisfyingthe conditions below while nearly maintaining their primary particleshapes and a part of particles of said agglomerates are not adhered tosaid fibrous substrate:

[0033] Average particle diameter (D) 100≦D≦3000 μm

[0034] Average relative displacement of the direction by directionanalysis (θ)10≦θ≦25

[0035] Frequency analysis 5 Hz/20 Hz intensity ratio (k) 0.6≦k≦0.9

[0036] Agglomerate maximum length (L)/minimum length (l) ratio1.2≦L/l≦15.0.

[0037] The present invention also provides a water-absorbing articlecontaining a water-absorbing material having water-absorbing polymerparticles immobilized on one side of a fibrous substrate so that saidwater-absorbing polymer particles absorb aqueous liquids through saidfibrous substrate, wherein immobilization of said water-absorbingpolymer particles is carried out by forming droplets of a reactionmixture initialized by mixing an aqueous solution of a polymerizablemonomer giving a water-absorbing polymer with a redox polymerizationinitiator in a gas phase, combining said droplets into agglomerateswhile nearly maintaining their primary particle shapes in the gas phaseand/or on a fibrous substrate, supporting said agglomerates formed inthe gas phase on said fibrous substrate, and then completingpolymerization of said agglomerates on said fibrous substrate toimmobilize said agglomerates on said fibrous substrate.

[0038] Water-absorbing composites, processes for preparingwater-absorbing composites and water-absorbing articles of the presentinvention are explained below in detail with reference to preferredembodiments, which are provided solely for purposes of illustration andare not intended to be limitative.

[0039] Water-Absorbing Composites

[0040] Water-absorbing composites of the present invention comprisewater-absorbing polymer particles immobilized on a fibrous substrate(hereinafter also simply referred to as “substrate”). A part ofwater-absorbing polymer particles contain primary particles having anaverage particle diameter of about 50-1000 μm, preferably about 100-900μm, more preferably about 200-800 μm. As used herein throughout, thesymbol “−” means a range defined by the recited figures both inclusiveas a minimum and a maximum.

[0041] Thirty % by weight or more, preferably about 50% or more, morepreferably about 80% or more of primary particles are combined to formagglomerates while maintaining their primary particle shapes. A part ofparticles forming agglomerates are not adhered to the fibrous substrate.That is, agglomerates consist of primary particles directly adhered tothe fibrous substrate and primary particles not adhered to the fibroussubstrate. Such agglomerates have a high water-absorbing speed becauseof the large specific surface area, while they have an excellentwater-absorbing capacity because only a part of primary particlesforming agglomerates are adhered to the fibrous substrate so that thefibrous substrate imposes less constraints on swelling with absorbedwater. Moreover, agglomerates are scarcely broken into primary particlesand separated from the fibrous substrate before and even after absorbingwater because joint surfaces of primary particles forming agglomeratesare fused together.

[0042] Agglomerates are characterized by a specific range of averageparticle diameter (D), average relative displacement of the direction bydirection analysis (θ), frequency analysis 5 Hz/20 Hz intensity ratio(k) and agglomerate maximum length (L)/minimum length (l) ratio asdefined above. Agglomerates have an average particle diameter (D) ofabout 100-3000 μm, preferably about 200-2000 μm, more preferably about250-2000 μm. If the average particle diameter is smaller than 100 μm,water-absorbing performance is not sufficiently shown. If the averageparticle diameter is greater than 3000 μm, adhesion to the fibroussubstrate decreases.

[0043] Average relative displacement of the direction by directionanalysis (θ) is about 10-25, preferably about 12-24, more preferablyabout 14-22. Frequency analysis 5 Hz/20 Hz intensity ratio (k) is about0.6-0.9, preferably about 0.65-0.85, more preferably about 0.65-0.80.Agglomerate maximum length (L)/minimum length (l) ratio is about1.2-15.0, preferably about 1.5-10.0, more preferably about 1.5-8.0.These average particle diameter (D), average relative displacement ofthe direction by direction analysis (θ), frequency analysis 5 Hz/20 Hzintensity ratio (k) and agglomerate maximum length (L)/minimum length(l) ratio can be determined by the methods described later in testexamples.

[0044] Water-absorbing composites of the present invention arecharacterized by their ability to maintain a soft touch because primarypolymer particles in the form of a true sphere are combined togetherwith secondary particles which are unangular in the form of grapes. Awater-absorbing composite containing a water-absorbing polymerimmobilized on a fibrous substrate similarly to the present inventionhas been developed and disclosed in JP-A 67403/97, but thewater-absorbing resin in the composite described therein consists ofangular and irregular single particles adhered to fibers so that skintouch is rough or prickly but not soft. On the contrary, thewater-absorbing composites of the present invention provide a greatlyimproved skin touch sensation.

[0045] Water-absorbing polymer particles are contained inwater-absorbing composites normally in an amount of about 50-300 g/m²,preferably about 100-250 g/m², especially about 130-220 g/m². If thecontent of water-absorbing polymer particles is low, water-absorbingcapacity is, of course, low. Excessive contents are uneconomic anddecrease the proportion of primary particles adhered to the fibroussubstrate to lower adhesion to the substrate.

[0046] Processes for preparing water-absorbing composites of the presentinvention are not specifically limited. Water-absorbing compositesprepared by any processes are included in the scope of the presentinvention so far as they satisfy the claimed conditions. Materials ofwater-absorbing polymer particles and fibrous substrates formingwater-absorbing composites of the present invention are not specificallylimited, either. Therefore, known water-absorbing polymers and fibroussubstrates can be used. A plurality of materials can be used incombination. Specific examples of water-absorbing polymers and fibroussubstrates will be described later. In water-absorbing composites of thepresent invention, water-absorbing polymers may be immobilized on eitheronly one side or both sides of a fibrous substrate, depending on thepurpose of the water-absorbing composites. For example, water-absorbingpolymers can be immobilized on both sides of a fibrous substrate toincrease the basic weight on the fibrous substrate or share functionsbetween both sides.

[0047] Processes for Preparing Water-Absorbing Composites

[0048] Water-absorbing composites suitable for the purpose of thepresent invention can be simply and economically prepared by processesof the present invention. Processes of the present invention compriseforming droplets of a reaction mixture initialized by mixing an aqueoussolution of a polymerizable monomer giving a water-absorbing polymerwith a redox polymerization initiator in a gas phase, combining saiddroplets into agglomerates while nearly maintaining their primaryparticle shapes in the gas phase and/or on a fibrous substrate,supporting said agglomerates formed in the gas phase on said fibroussubstrate, and then completing polymerization of said agglomerates onsaid fibrous substrate to immobilize said agglomerates on said fibroussubstrate.

[0049] Polymerizable Monomers

[0050] Polymerizable monomers used in the present invention may be ofany type so far as they give a water-absorbing polymer and areinitialized with a redox polymerization initiator. These monomers mustbe water-soluble because they are used as aqueous solutions, thoughmonomers giving a water-absorbing polymer are normally water-soluble.

[0051] Typical examples of these monomers preferably suitable for use inthe present invention are aliphatic unsaturated carboxylic acids orsalts thereof, specifically unsaturated monocarboxylic acids or saltsthereof such as acrylic acid or salts thereof, methacrylic acid or saltsthereof, or unsaturated dicarboxylic acids or salts thereof such asmaleic acid or salts thereof, itaconic acid or salts thereof, which maybe used alone or in combination.

[0052] Among these, acrylic acid or salts thereof and methacrylic acidor salts thereof are preferred, with especially preferred being acrylicacid or salts thereof. Polymerizable monomers giving a water-absorbingpolymer in the present invention are preferably aliphatic unsaturatedcarboxylic acids or salts thereof as described above, therefore, aqueoussolutions of these polymerizable monomers are preferably aqueoussolutions essentially containing an aliphatic unsaturated carboxylicacid or a salt thereof. As used herein, the expression “essentiallycontaining an aliphatic unsaturated carboxylic acid or a salt thereof”means that the aliphatic unsaturated carboxylic acid or a salt thereofis contained at 50 mol % or more, preferably 80 mol % or more on thebasis of the total amount of the polymerizable monomer.

[0053] Suitable salts of aliphatic unsaturated carboxylic acids normallyinclude water-soluble salts such as alkali metal salts, alkali earthmetal salts, ammonium salts or the like. The neutrality is appropriatelyselected depending on the purpose, but 20-90 mol % of carboxyl group ispreferably neutralized with an alkali metal salt or an ammonium salt inthe case of acrylic acid. If the partial neutrality of an acrylicmonomer is less than 20 mol %, the resulting water-absorbing polymertends to have much low water-absorbing capacity.

[0054] Acrylic monomers can be neutralized with alkali metal hydroxidesor bicarbonates or ammonium hydroxide or the like, preferably alkalimetal hydroxides such as sodium hydroxide and potassium hydroxide.

[0055] In addition to said aliphatic unsaturated carboxylic acids,monomers copolymerizable with them such as (meth)acrylamide,(poly)ethylene glycol (meth)acrylate, 2-hydroxyethyl (meth)acrylate oreven slightly water-soluble monomers including acrylic alkyl esters suchas methyl acrylate or ethyl acrylate may also be copolymerized in anamount within a range that does not affect performance of the resultingwater-absorbing polymers in the present invention. As used herein, theterm “(meth)acryl” means both “acryl” and “methacryl”.

[0056] Among these polymerizable monomers, those giving awater-absorbing polymer may also be used as main monomers of “an aqueoussolution of a polymerizable monomer giving a water-soluble polymer”rather than auxiliary components to aliphatic unsaturated carboxylicacids or salts thereof.

[0057] Aliphatic unsaturated carboxylic acids or salts thereof,especially acrylic acid or salts thereof sometimes form aself-crosslinked polymer by themselves, but may be positively induced toform a crosslinked structure using a crosslinker. The use of acrosslinker normally improves water-absorbing performance of theresulting water-absorbing polymer. Preferably, suitable crosslinkersinclude divinyl compounds copolymerizable with said polymerizablemonomers such as N,N′-methylenebis(meth)acrylamide, (poly)ethyleneglycol (meth)acrylate and water-soluble compounds having two or morefunctional groups capable of reacting with a carboxylic acid includingpolyglycidyl ethers such as ethylene glycol diglycidyl ether,polyethylene glycol diglycidyl ether. Among them,N,N′-methylenebis(meth)acrylamide is especially preferred. Crosslinkersare used in an amount of 0.001-1% by weight, preferably 0.01-0.5% byweight on the basis of the amount of the monomer.

[0058] The concentration of polymerizable monomers in an aqueouspolymerizable monomer solution essentially containing an aliphaticunsaturated carboxylic acid or a salt thereof as described above is 20%or more, preferably 25% or more. Concentrations less than 20% by weightare not preferred because droplets having an appropriate viscosity aredifficult to produce whereby the resulting water-absorbing polymer hasinsufficient water-absorbing capacity. The upper limit is preferablyabout 80% by weight in respect of handling of the polymerizationreaction solution.

[0059] Redox Polymerization Initiators

[0060] Polymerization initiators used in the present invention should besomewhat water-soluble redox systems combining an oxidizing radicalgenerator and a reducing agent. Such oxidizing agents include hydrogenperoxide, persulfates such as ammonium persulfate or potassiumpersulfate, peroxides including hydroperoxides such as t-butylhydroperoxide or cumene hydroperoxide, secondary cerium salts,permanganates, chlorites, hypochlorites, etc., among which hydrogenperoxide is especially preferred. These oxidizing agents are used in anamount of about 0.01-10% by weight, preferably about 0.1-2% by weight onthe basis of polymerizable monomers.

[0061] Suitable reducing agents are capable of forming a redox systemwith said oxidizing agents, specifically sulfites such as sodium sulfiteor sodium hydrogensulfite, sodium thiosulfate, cobalt acetate, coppersulfate, ferrous sulfate, L-ascorbic acid or L-ascorbic acid alkalimetal salts, etc. Among others, L-ascorbic acid or L-ascorbic acidalkali metal salts are especially preferred. These reducing agents areused in an amount of about 0.00-10% by weight, preferably about 0.01-2%by weight on the basis of polymerizable monomers.

[0062] Polymerization Processes

[0063] In the present invention, an aqueous solution of a polymerizablemonomer giving a water-absorbing polymer, specifically an aqueoussolution of a polymerizable monomer essentially containing an aliphaticunsaturated carboxylic acid or a salt thereof is initialized with aredox polymerization initiator and, after initiation of the reaction,the reaction mixture under polymerization containing the monomer and theproduced polymer is divided into droplets in a gas phase and thedroplets are combined into agglomerates in the gas phase and/or on afibrous substrate, and then polymerization of the agglomerates iscompleted on the fibrous substrate. Thus, polymerization is completedafter the agglomerates are supported on said fibrous substrate(optionally supporting the agglomerates) if they are formed in a gasphase or directly completed if they are formed on the fibrous substrate.As used herein, the expression “on a fibrous substrate” includes on theface of a shaped fibrous substrate, on fibers of the substrate and onthe inner faces of spaces between fibers of the substrate.

[0064] In this polymerization format, it is necessary to selectoperating conditions which allow the initiated monomer-containingaqueous solution to form droplets having a determined viscosity toproduce agglomerates and firmly adhere them to the substrate, takinginto much account that polymerization is initialized substantially assoon as a redox system is formed in the presence of the monomer and thatthe polymerization initiated with the redox polymerization initiator isa chain polymerization, and correspondingly that the time to reach adesired polymerization degree or the time for the monomer-containingaqueous solution to reach a desired level of viscosity is relativelyshort.

[0065] Under these considerations, a preferred method comprisesinitiating polymerization by mixing a first solution consisting of anaqueous polymerizable monomer solution containing either one of anoxidizing agent or a reducing agent forming a redox polymerizationinitiator and a second solution consisting of an aqueous solutioncontaining the other component of the redox polymerization initiator andoptionally the polymerizable monomer in a gas phase.

[0066] Specifically, the first and second solutions are discharged fromseparate nozzles in such a manner that they collide with each other in aliquid column state at a crossing angle of about 15° or more. Thus, bothsolutions are collided at some crossing angle so that a part of theenergy produced by discharging from nozzles is used for mixing. Thecrossing angle between the first and second solutions discharged fromthe respective nozzles is appropriately chosen depending on theproperties of the polymerizable monomer used, the flow rate ratio orother factors. For example, the crossing angle may be small if thelinear velocity of the solutions is high. The angle should be about 15°or more, preferably about 20° or more for attaining sufficient mixingeffect. The upper limit of the angle is not specifically limited so faras a liquid column is formed after the first and second solutionscollide with each other (as detailed later), but the maximum angle isabout 120° or less, preferably about 100° or less for industrialapparatus.

[0067] In this method, the first and second solutions exiting therespective nozzles must be collided in a liquid column state so thatboth solutions combine to form a liquid column. The solutions thuscollided in a liquid state can be mixed in a selected flow rate ratio toachieve a good polymerization reaction. If the first and secondsolutions are collided after they have formed particles, favorableresults are hardly obtained because the mixing ratio shifts from theselected flow rate ratio. The distance between nozzle tips can be freelydetermined within the range that allows fluids to be collided in aliquid column state, and nozzle tips may be in contact with each other.Nozzles may have an inner diameter appropriately chosen depending on theproperties of the polymerizable monomer used and the shape of theintended water-absorbing composite, preferably in the range of about0.15-2.0 mm, more preferably about 0.1-1.0 mm.

[0068] In this case, the temperature of the first solution is normallyordinary temperatures to about 60° C., preferably ordinary temperaturesto about 40° C., and the temperature of the second solution is alsonormally ordinary temperatures to about 60° C., preferably ordinarytemperatures to about 40° C.

[0069] Thus, the aqueous solutions discharged from the respectivenozzles are collided in a liquid column state to combine into onestream. The combined solutions form a liquid column and maintain thisstate for a period, and then this liquid column is broken into droplets.The resulting droplets fall in a gas phase or on a substrate to formagglomerates there.

[0070] The period for which the combined solutions form and maintain aliquid column, the height of the liquid column and the sizes of dropletsdepend on selected conditions such as the inner diameters of nozzles,but normally said period is about 0.1-3 seconds, the height of theliquid column is about 3-50 mm, and the sizes of droplets are about5-3000 μm in diameter. Especially, the sizes of droplets are preferablyin a range of about 50-1000 μm in order that polymerization of dropletsproceeds to combine them into appropriate agglomerates.

[0071] The gas phase providing a place in which polymerization isinitiated and droplets are formed during polymerization is preferably agas inert to the polymerization such as nitrogen, helium, carbondioxide, but may also be air. The humidity in the gas is notspecifically limited and the gas may wholly consist of water vapor, butif the humidity is too low, moisture in the aqueous monomer solutionevaporates to precipitate the monomer before polymerization proceeds,with the result that polymerization speed may be much lowered orpolymerization may stop halfway. The temperature condition of the gas isroom temperature or more but about 150° C. or less, preferably about100° C. or less. The direction of gas flow may be either parallel orcounter to the travel direction of the liquid column and droplets, butcounter flow (counter-gravity direction) is preferred when droplets arerequired to stay longer in a gas phase or when the polymerization degreeof the polymerizable monomer, and therefore the viscosity of dropletsshould be increased.

[0072] As polymerization proceeds, droplets collide with each other tocombine into agglomerates while nearly maintaining their primaryparticle shapes in a gas phase or on a fibrous substrate, and thenpolymerization of agglomerates is directly completed if they are formedon the fibrous substrate or completed on the fibrous substrate after theagglomerates are supported on said fibrous substrate if they are formedin the gas phase, whereby said agglomerates are immobilized on saidfibrous substrate in such a manner that they surround or touch fibers ofsaid substrate. At least a part of particles of agglomerates immobilizedon said fibrous substrate form agglomerates joined together whilemaintaining their particle shapes, and other particles of agglomeratesare not adhered to the fibrous substrate.

[0073] Various conditions should be selected so that the polymerizationdegree may be about 20-97% , preferably about 30-97% , more preferablyabout 50-95% when droplets under polymerization form agglomerates in agas phase or on a substrate. If the polymerization degree is too low,droplets cannot be adhered in the form of agglomerates to the substratebecause even droplets colliding with each other in a gas phase combineinto gross particles without forming agglomerates or droplets falling onthe substrate spread or are absorbed or impregnated into the substrate.If the polymerization degree is too high, adhesion to the substrate isnot ensured and adhesion between the substrate and the water-absorbingpolymer is affected.

[0074] The polymerization degree and agglomeration can be controlled bymodulating the crossing angle between the first and second solutionsdischarged from nozzles, the diameters of nozzles, the nature and amountof the polymerization initiator, the distance between nozzles and thesubstrate, the temperature and humidity of the gas phase, the number andconfiguration of nozzles, and the relative position or distance betweennozzles and the substrate to increase the probability of collisionbetween solutions or adjust the polymerization level in the gas phase.Other methods than using two opposed nozzles may also be used, such as,for example, a bundle type nozzle sprayer having two nozzles withaligned tips, or a double nozzle sprayer in which one nozzle is insertedinto the other nozzle.

[0075] Components of solutions discharged from the respective nozzlescollide and mix with each other in a liquid column state and then formdroplets, which are polymerized into agglomerates during or afterfalling on a substrate, whereby a final polymerization stage proceeds onthe substrate.

[0076] If desired, unreacted monomers remaining in agglomerates may betreated to react them, by means of 1) promoting polymerization of themonomers, 2) directing the monomers into other derivatives, or 3)removing the monomers.

[0077] Means of 1) promoting polymerization of the monomers include, forexample, further heating the composite of agglomerates and a substrate,or adding a catalyst or a catalytic element which promotespolymerization of the monomers to agglomerates and then heating them, orirradiating the composite with UV rays, electromagnetic radiations orparticulate ionizing radiations, etc.

[0078] The method of further heating the composite of agglomerates and asubstrate involves heating the composite of agglomerates and a substrateat about 100-250° C. to polymerize monomers remaining in theagglomerates.

[0079] The method of adding a catalyst or a catalytic element whichpromotes polymerization of the monomers to agglomerates involves addinga solution of a reducing agent to agglomerates when a redoxpolymerization initiator is used for polymerization, for example,because the radical generator frequently remain. Suitable reducingagents are sodium sulfite, sodium hydrogensulfite, L-ascorbic acid orthe like used as redox polymerization initiators, and they may benormally added as aqueous 0.5-5% by weight solutions to agglomerates.Reducing agents may be added in an amount of 0.1-2% by weight on thebasis of dry resin. Reducing agents may be added by any method such asspraying with an atomizer or immersing into a reducing agent insolution. After a reducing agent is added, agglomerates are then heatedto polymerize polymerizable monomers. Heating may be carried out at100-150° C. for about 10-30 minutes, for example. This heating lowersthe moisture content of agglomerates, but if the moisture content isstill high, the agglomerates are further dried in a dryer to give aproduct water-absorbing composite.

[0080] The method of irradiating a composite of agglomerates and asubstrate with UV rays involves using ordinary UV lamps. The irradiationintensity, irradiation period or other conditions depend on the natureof the fibrous substrate, the impregnation level of the remainingmonomers or other factors, but irradiation normally takes place with UVlamps at about 10-200 W/cm, preferably about 30-120 W/cm for anirradiation period of about 0.1 second −30 minutes at a lamp-compositedistance of 2-30 cm. The moisture content of the composite here isnormally about 0.01-40 parts by weight, preferably about 0.1-1.0 partsby weight per 1 part by weight of the polymer. Moisture contents lessthan 0.01 parts by weight or more than 40 parts by weight are notpreferred because they greatly affect reduction of remaining monomers.UV irradiation may be performed in a vacuum, or in the presence of aninorganic gas such as nitrogen, argon or helium, or in the air. Theirradiation temperature is not specifically limited, and the intendedpurpose can be sufficiently achieved at room temperature. The UVirradiation apparatus used is not specifically limited, either, but anymethod can be applied such as stationary irradiation for a determinedperiod or continuous irradiation on a belt conveyor.

[0081] The method of irradiating a composite of agglomerates and asubstrate with radiations involves using high-energy radiations such asaccelerated electrons or gamma rays. The dose to be applied depends onthe amount of remaining monomers in the composite, the moisture contentor the like, but normally ranges from about 0.01 to 100 Mrad, preferablyabout 0.1 to 50 Mrad. If the dose exceeds 100 Mrad, water-absorbingcapacity is much low. If the dose is less than 0.01 Mrad, it isdifficult to obtain a desired composite having high water-absorbingcapacity or water-absorbing speed and much reduced remaining monomers.The moisture content in the composite here is normally 40 parts byweight or less, preferably 10 parts by weight or less per 1 part byweight of the fibrous substrate. Moisture contents in excess of 40 partsby weight are not preferred because water-absorbing speed is lessimproved and especially, reduction of remaining monomers is greatlyaffected. According to the present invention, the composite may beirradiated with a high-energy radiation in a vacuum, or in the presenceof an inorganic gas such as nitrogen, argon or helium, or in the air. Apreferred atmosphere is the air, and if irradiation is performed in theair, water-absorbing capacity or water-absorbing speed is increased andremaining monomers are remarkably reduced. The irradiation temperatureis not specifically limited, and the intended purpose can besufficiently achieved at room temperature.

[0082] Means of 2) directing the monomers into other derivativesinclude, for example, adding an amine, ammonia or the like or a reducingagent such as hydrogensulfites, sulfites, pyrosulfites or the like.

[0083] Means of 3) removing the monomers include, for example,extraction with an organic solvent or distillation. Extraction with anorganic solvent involves immersing a composite of agglomerates and asubstrate into an aqueous organic solvent to extract off the remainingmonomers. Suitable aqueous organic solvents include ethanol, methanol,acetone or the like preferably having a moisture content of about 10-99%by weight, especially about 30-60% by weight. Generally, the higher themoisture content, the higher the ability of removing remaining monomers,but energy consumption increases during the subsequent drying step ifaqueous organic solvents having a high moisture content are used. Theperiod for which the composite of agglomerates and a substrate isimmersed in an aqueous organic solvent may be normally about 5-30minutes, and it is also preferable to use a means of promotingextraction of remaining monomers such as rocking the composite ofagglomerates and a substrate. After immersion, the composite may bedried in a dryer.

[0084] Distillation of the monomers involves treating the composite ofagglomerates and a substrate with overheated water vapor or a watervapor-containing gas. For example, saturated water vapor of 110° C. canbe heated to about 120-150° C. and brought into contact with a compositeof agglomerates and a substrate as overheated water vapor to reduce theremaining monomers in the agglomerates. According to this method, it isthought that the remaining monomers can also be vaporized off from theagglomerates when water in the agglomerates evaporates as water vapor.This method combines the step of removing the remaining monomers withthe step of drying the product.

[0085] For the purpose of improving water-absorbing performance, thesurfaces of agglomerates on the substrate can be crosslinked with acrosslinker. Generally, it is known to improve characteristics of resinparticles by adding a crosslinker on the surfaces of powderywater-absorbing resin particles and then crosslinking the surfaces byheating, and it is thought that these particles can maintain theirshapes without receiving inhibition against swelling with water absorbedbecause crosslinked structures are selectively formed on the surfaces.This process begins with adding a surface crosslinker in solution toagglomerates of a composite of agglomerates and a substrate. Suitablesurface crosslinkers are polyfunctional compounds copolymerizable withpolymerizable monomers such as N,N′-methylenebis(meth)acrylamide orpoly)ethylene glycol bis(meth)acrylate, or compounds having a pluralityof functional groups capable of reacting with carboxylate group such as(poly)ethylene glycol diglycidyl ether. These surface crosslinkers arenormally used in an amount of about 0.1-1% by weight, preferably about0.2-0.5% by weight on the basis of agglomerates (dry basis). Thesesurface crosslinkers are preferably used as solutions diluted at about0.1-1% by weight, especially about 0.2-0.5% by weight in water, ethanol,or methanol, for example, so that they may be uniformly dispensed on theentire surfaces of agglomerates. Preferably, crosslinkers in solutionare dispensed normally by using an atomizer to spray a crosslinkersolution on agglomerates, or using a roll brush immersed at the base ina tank containing a crosslinker solution to apply the crosslinkersolution on a composite of agglomerates and a substrate while it isbeing moved with the side to be coated with resin particles facingdownward. After a crosslinker solution is excessively applied, an excessof the crosslinker solution may be removed by air blasting or mildlypressing the composite between pressure rolls without crushing resinparticles. These crosslinker solutions may be applied at roomtemperature. After a crosslinker solution is added, the composite ofagglomerates and a substrate is then heated to promote crosslinkingreaction to selectively form crosslinked structures on the surfaces ofagglomerates. Conditions for the crosslinking reaction may beappropriately selected depending on the crosslinker used, but thereaction is normally performed at a temperature of 100° C. or more for10 minutes or more.

[0086] Water-absorbing composites prepared by a process of the presentinvention have excellent water-absorbing properties and a highwater-absorbing speed, and most of the highly water-absorbing polymer isstably immobilized on the fibrous substrate, and the immobility ofswollen gel after absorbing water is also excellent. A prior art relatedto the present invention, JP-A 239912/97, discloses a process forpreparing a water-absorbing composite comprising providingwater-absorbing polymer particles immersed with a water-solubleethylenically unsaturated monomer on a fibrous substrate or a substrateand then polymerizing the ethylenically unsaturated monomer in saidwater-absorbing polymer particles to immobilize the water-absorbingpolymer particles on said fibrous substrate or said substrate. In thisprocess, fibers in the fibrous substrate are point-bonded to thesurfaces of primary particles of agglomerates because thewater-absorbing resin polymer particles used have been completelypolymerized. On the contrary, the present invention intends to bondincompletely polymerized particles to fibers in the fibrous substrate sothat the fibers in the fibrous substrate penetrate into a part ofprimary particles of agglomerates. As compared with JP-A 239912/97,water-absorbing resins of water-absorbing composites of the presentinvention have remarkably improved bonding strength during waterabsorption as evident from the bonding mechanism.

[0087] Fibrous Substrates

[0088] The fibrous substrate to which said droplets or agglomerates ofthe reaction mixture under polymerization are to be adhered ispreferably a shaped fibrous substrate. As used herein, the shapedfibrous substrate specifically means a woven or nonwoven or knittedfabric consisting of loosely shaped fibers in a specific form such as apad, carded or air-laid web, tissue paper, cotton gauze, etc., which mayrequire cutting, joining, shaping or other processes but no moreweb-forming process to incorporate the fibrous substrate into anarticle.

[0089] Fibers forming the substrate are preferably hydrophilic fiberssuch as wood pulp, rayon, cotton, regenerated cellulose or othercellulose fibers because they are used in water-absorbing articles, andthese fibers derive the greatest benefit from the present invention andsubstrates based on such a hydrophilic fiber are especially preferred inthe present invention. Other suitable fibrous substrates are based onpolyester fibers or other classes of non-hydrophilic fibers such aspolyethylene, polypropylene, polystyrene, polyamide, polyvinyl alcohol,polyvinyl chloride, polyvinylidene chloride, polyacrilonitrile,polyurea, polyurethane, polyfluoroethylene, polyvinylidene cyanidefibers. Relatively dense fibrous substrates made of paper, wood, backskin, leather or the like may also be used.

[0090] Preparation of Water-Absorbing Composites

[0091] A process for practically preparing a water-absorbing compositeis illustrated as follows. A liquid column of a reaction mixture underpolymerization initiated with an aqueous polymerizable monomer solutionis fallen on a sheet of said fibrous substrate which is being moved on abelt conveyor, and the resulting droplets are combined in a gas phase oron the fibrous substrate sheet to form agglomerates, which are thensupported on said substrate sheet for a period to completepolymerization. The resulting water-absorbing polymer containingmoisture is dried to remove the moisture, whereby a web ofwater-absorbing composite is obtained. This is cut into desired shapeand size to give a water-absorbing composite product.

[0092] Water-Absorbing Composite

[0093] Thus obtained water-absorbing composite comprises awater-absorbing polymer in the form of agglomerates supported on afibrous substrate in such a manner that at least a part of theagglomerates are immobilized on the fibrous substrate to surround ortouch fibers of the substrate and the fibers penetrate into a part ofprimary particles. Therefore, said polymer is firmly immobilized on thefibrous substrate not only before water is absorbed but also after it isgelled with water absorbed. Moreover, joint surfaces of primaryparticles forming agglomerates are fused together without any bondinginterface so that agglomerates are excellent in keeping their shapes asabsorbing materials less liable to return to single particles even afterthey are swollen with water absorbed. Such a water-absorbing polymer ofthe present invention is characterized by the low possibility ofseparation after absorbing water, as evident from the supporting raterepresenting the supporting strength of the water-absorbing polymer on afibrous substrate described later.

[0094] Water-absorbing composites of the present invention are alsocharacterized by excellent water-absorbing capacity because thewater-absorbing polymer is in the form of agglomerates and a part ofprimary particles forming the agglomerates are not adhered to fibers ofthe substrate, whereby said polymer is less constrained by substratefibers and less hindered by the fibers from being swollen with waterabsorbed.

[0095] Water-absorbing composites of the present invention also havesatisfactory performance in water-absorbing capacity and water-absorbingspeed as evident from physiological saline-absorbing capacity andabsorbing speed tests described in the examples (and comparativeexamples) later. According to the present invention, water-absorbingcapacity is typically 20 (times) or more, normally 30 (times) or more,often 35 (times) or more. Water-absorbing speed is typically 15 g/5 minor more, normally 20 g/5 min or more, often 25 g/5 min or more.

[0096] Water-absorbing composites of the present invention are alsosatisfactory in respect of their low residual unreacted monomer level.According to the present invention, the residual unreacted monomer levelis typically 500 ppm or less, normally 300 ppm or less, often 100 ppm orless.

[0097] Water-absorbing composites of the present invention can be usedfor the same purposes as those of conventional water-absorbing resins.They can be appropriately used for various purposes of water-absorbingresins as introduced in “Water-absorbing polymers”, pp. 81-111 (Masuda,Kyoritsu Shuppan, 1987); “Trend of development and applications ofhighly water-absorbing resins” (Omori, Technoforum, 1987); Tanaka in“Industrial materials”, Vol. 42, No. 4, pp. 18-26, 1994; and Harada etal. ditto, pp. 26-30; such as paper diapers, sanitary goods,freshness-keeping materials, moisture-retaining materials,low-temperature insulating materials, anti-sweating materials,soil-improving materials, etc.

[0098] They can also be used for the purposes of sheet-likewater-absorbing composites as proposed in JP-A 267370/88, 10667/88,295251/88, 270801/88, 294716/88, 64602/89, 231940/89, 243927/89,30522/90, 153731/90, 21385/91, 133728/92, or 156118/99, for example.

[0099] Water-Absorbing Articles

[0100] Water-absorbing articles of the present invention comprise awater-absorbing material having water-absorbing polymer particlesimmobilized on one side of a fibrous substrate (hereinafter sometimessimply referred to as “water-absorbing material”) so that saidwater-absorbing polymer particles absorb aqueous liquids through saidfibrous substrate, characterized in that a water-absorbing composite ofthe present invention described above or a water-absorbing compositeprepared by a process of the present invention described above is used.Among water-absorbing composites, those having water-absorbing polymerparticles immobilized on one side of a fibrous substrate are hereinspecifically called water-absorbing materials.

[0101] Water-absorbing articles of the present invention essentiallycomprise a fibrous substrate and a water-absorbing polymer, i.e. awater-absorbing material having a water-absorbing polymer immobilized ononly one side of a fibrous substrate, appropriately combined withmaterials commonly used in water-absorbing articles such as fluffy pulp,paper, nonwoven fabric, polyolefin films, etc. The water-absorbingmaterial here is arranged in such a manner that a water-absorbing faceis provided on the fibrous substrate side. Thus, aqueous liquids to beabsorbed pass through the fibrous substrate of the water-absorbingmaterial to reach water-absorbing polymer particles. This ensures that awater-absorbing article which allows rapid absorption and hardlyreleases the absorbed aqueous liquids even under pressure can beobtained.

[0102] Similarly to water-absorbing articles, especially so-called paperdiapers or sanitary napkins using a bulking material such as fluffy pulpto improve body fit during use, water-absorbing articles of the presentinvention preferably have a layer of a bulking material such as fluffypulp. The fluffy pulp layer is preferably provided on thewater-absorbing polymer side at a basic weight of 80-250 g/m²,especially 100-220 g/m². When a fluffy pulp layer is provided on eachside of a water-absorbing material, the basic weight is preferablyhigher on the water-absorbing polymer side than the fibrous substrateside. If a fluffy pulp layer having a higher basic weight is provided onthe fibrous substrate side, aqueous liquids to be absorbed are absorbedmore slowly to the main absorbent water-absorbing material because theypass through the hydrophilic fluffy pulp layer to reach thewater-absorbing material. Contrary to the water absorbed inwater-absorbing polymer particles, the water absorbed in fluffy pulp isreadily released so that it is readily removed when the water-absorbingarticle is pressed after absorbing water.

[0103] Additives

[0104] Water-absorbing polymers, water-absorbing composites orwater-absorbing articles may contain various additives to provide adesired function depending on the intended purpose. These additivesinclude stabilizers for preventing polymer decomposition or denaturationby liquids absorbed, antibacterial agents, deodorants, deodorizers,fragrances, foaming agents, etc.

[0105] Stabilizers for preventing polymer decomposition or denaturationby liquids absorbed include stabilizers for preventing decomposition ordenaturation of water-absorbing resins by excreta (i.e. human urine orfeces) or biological liquids (such as human blood, menstrual blood,secreted liquids). JP-A 118375/88 proposes a method for incorporating anoxygen-containing reducing inorganic salt and/or an organic antioxidantinto a polymer; JP-A 153060/88 proposes a method for incorporating anoxidizing agent; JP-A 127754/88 proposes a method for incorporating anantioxidant; JP-A 272349/88 proposes a method for incorporating asulfur-containing reducing agent; JP-A 146964/88 proposes a method forincorporating a metal chelating agent; JP-A 15266/88 proposes a methodfor incorporating a radical chain inhibitor; JP-A 275661/89 proposes amethod for incorporating a phosphinate-or phosphonate-containing aminecompound or a salt thereof; JP-A 29257/89 proposes a method forincorporating a polyhydric metal oxide; JP-A 255804/90 and 179008/91propose a method for performing polymerization in the presence of awater-soluble chain transfer agent, etc. Materials and methods describedin JP-A 306202/96, 53884/95, 62252/95, 113048/95, 145326/95, 145263/95,228788/95 and 228790/95 are also suitable. Specific examples include,for example, potassium titanate oxalate, tannic acid, titanium oxide,amine phosphinates (or salts thereof), amine phosphonates (or saltsthereof), metal chelates, etc. Particularly, stabilizers against humanurine, human blood and menstrual blood are sometimes called human urinestabilizers, human blood stabilizers and menstrual blood stabilizers,respectively.

[0106] Antibacterial agents are used to prevent spoiling by liquidsabsorbed. Suitable antibacterial agents can be appropriately selectedfrom those introduced in, for example, “New development ofbacteriocidal/antibacterial techniques”, pp. 17-80 (Toray ResearchCenter (1994)), “Test/evaluation methods and product designs ofantibacterial/antifungal agents” pp. 128-344 (NTS (1997)), JapanesePatent No. 2760814, JP-A 179114/64, 31425/81, 25813/82, 189854/84,105448/84, 155861/85, 181532/86, 135501/88, 139556/88, 156540/88,5546/89, 5547/89, 153748/89, 221242/89, 253847/90, 59075/91, 103254/91,321141/91, 11948/92, 92664/92, 138165/92, 266947/92, 9344/93, 68694/93,161671/93, 179053/93, 269164/93, and 165981/95.

[0107] Suitable examples include, for example, alkyl pyridinium salts,benzalkonium chloride, chlorhexidine gluconate, zinc pyrithione, silverinorganic powders, etc. Typical examples of quaternary nitrogenantibacterial reagents include methylbenzethonium chloride, benzalkoniumchloride, dodecyltrimethylammonium bromide, tetradecyltrimethylammoniumbromide and hexadecyltrimethylammonium bromide. Heterocyclic quaternarynitrogen antibacterial reagents include dodecylpyridinium chloride,tetradecylpyridinium chloride, cetylpyridinium chloride (CPC),tetradecyl-4-ethylpyridinium chloride and tetradecyl-4-methylpyridiniumchloride.

[0108] Other preferred antibacterial reagents are bis-biguanides, whichare also known as antibacterial reagents. These are described in detailin U.S. Pat. Nos. 2,684,924, 2,990,425, 2,830,006 and 2,863,019, forexample. The most preferred bisguanide is1,6-bis(4-chlorophenyl)diguanide hexane, which is known as chlorhexidineand water-soluble salts thereof. Especially preferred are hydrochloride,acetate and gluconate of chlorhexidine.

[0109] Some other types of antibacterial reagents are also useful, suchas carbanilides, substituted phenols, metal compounds and rare earthsalts of surfactants. Carbanilides include 3,4,4′-trichlorcarbanilide(TCC, trichlocarban) and 3-(trifluoromethyl)-4,4′-dichlorcarbanilide(IRGASAN). Substituted phenols include5-chloro-2-(2,4-dichlorophenoxy)phenol (IRGASAN DP-300). Metal compoundsinclude salts of graphite and tin, such as zinc chloride, zinc sulfideand tin chloride. Rare earth salts of surfactants are disclosed inEuropean Patent Publication No. 10819. This type of rare earth saltsinclude lanthanum salts of straight C10-18 alkylbenzenesulfonates.

[0110] Deodorants, deodorizers and fragrances are used to prevent orreduce unpleasant odors of liquids absorbed. Suitable deodorants,deodorizers and fragrances can be appropriately selected from thoseintroduced in, for example, “Technology and outlook for newdeodorants/deodorizers” pp. 38-20 (Toray Research Center (1994)), JP-A105448/84, 158861/85, 181532/86, 153748/89, 221242/89, 265956/89,41155/90, 253847/90, 103254/91, 269164/93 and 277143/93. Specificexamples of deodorants/deodorizers include iron complexes, tea-extractedcomponents and activated carbon. Specific examples of fragrances includeperfume-type pyroligneous acids (citral, cynnamic aldehyde, heliotropin,camphor, bornyl acetate), paradichlorobenzene, surfactants, higheralcohols, terpenic compounds (limonene, pinene, camphor, borneol,eucalyptol, eugenol).

[0111] Foaming agents and foaming aids can be used to increasepores/surface areas for the purpose of improving water-absorbingperformance of water-absorbing resins. Suitable foaming agents andfoaming aids can be appropriately selected from those introduced in, forexample, “Additives for rubber/plastics” (Rubber Digest Co., 1989, pp.259-267). Specific examples include sodium bicarbonate, nitrosocompounds, azo compounds, sulfonyl hydrazides, etc.

[0112] These additives are appropriately added depending on the intendedpurpose and action mechanism during various steps of preparationprocesses of water-absorbing resins, water-absorbing composites andwater-absorbing articles. For example, foaming agents are suitably addedbefore or during polymerization in the preparation of water-absorbingresins. Human urine stabilizers, human blood stabilizers, antibacterialagents, deodorants and fragrances can be added during various steps ofpreparation processes of water-absorbing resins, water-absorbingcomposites and water-absorbing articles. Naturally, they may also bepreliminarily added to the fibrous substrate.

[0113] The present invention will now be further described by referenceto certain Examples which are provided solely for purposes of limitationand are not intended to be limitative.

EXAMPLES Example 1

[0114] To 125 parts by weight of an aqueous 80% by weight acrylic acidsolution were added 57.3 parts by weight of an aqueous 48.5% by weightsodium hydroxide solution, 6.4 parts by weight of water, 0.15 parts byweight of a crosslinker (N,N′-methylenebisacrylamide) and 5.0 parts byweight of an aqueous 30% by weight hydrogen peroxide solution as anoxidizing agent to prepare solution A having a monomer concentration of60% by weight and a neutrality of 50 mol %.

[0115] Separately, 57.3 parts by weight of an aqueous 48.5% by weightsodium hydroxide solution, 9.9 parts by weight of water, 0.15 parts byweight of a crosslinker (N,N′-methylenebisacrylamide) and 1.5 parts byweight of L-ascorbic acid as a reducing agent was added to 125 parts byweight of an aqueous 80% by weight acrylic acid solution to preparesolution B having the same monomer concentration and neutrality as thoseof solution A.

[0116] The prepared solutions A and B were mixed with nozzles shown inFIG. 1, having an inner diameter of 0.13 mm and consisting of 5 nozzlesfor each solution spaced at intervals of 1 cm. The crossing anglebetween solutions A and B discharged from nozzles was 30° and thedistance between nozzle tips of both solutions was 4 mm. Solutions A andB were warmed to 40° C. and pumped at a flow rate of 5 m/sec.

[0117] Solutions A and B were combined at the exit of the respectivenozzle pairs to form liquid columns of about 10 mm and then divided intodroplets to fall in a gas phase (in the air at a temperature of 50° C.)under polymerization. Some droplets collided with each other in the gasphase to form agglomerates, which fell on a polyester nonwoven fabricsubstrate (basic weight: 30 g/m²) placed 3 m below the nozzles tips tocomplete polymerization on the substrate. In parallel, some dropletsfell on said substrate to form agglomerates on the substrate, and thencomplete polymerization on said substrate. Thus, a water-absorbingpolymer was supported on said substrate. The assembly was dried to amoisture content of 5% in the supported polymer to give water-absorbingcomposite A having a supported polymer level of 200 g/m².

[0118] Light microphotographs of this water-absorbing composite A areshown in FIGS. 2 and 3, and a scanning electron microphotograph of thiswater-absorbing composite A shown in FIG. 4.

Example 2

[0119] The procedure of Example 1 was repeated except that solution Aused in Example 1 was replaced by a solution prepared by adding 80.4parts by weight of 48.5% by weight potassium hydroxide, 2.0 parts byweight of water, 0.15 parts by weight of a crosslinker(N,N′-methylenebisacrylamide) and 5.0 parts by weight of an aqueous 30%by weight hydrogen peroxide solution as an oxidizing agent to 125 partsby weight of an aqueous 80% by weight acrylic acid solution and solutionB used in Example 1 was replaced by a solution prepared by adding 80.4parts by weight of 48.5% by weight potassium hydroxide, 5.5 parts byweight of water, 0.15 parts by weight of a crosslinker(N,N′-methylenebisacrylamide) and 1.5 parts by weight of L-ascorbic acidas a reducing agent to 125 parts by weight of an aqueous 80% by weightacrylic acid solution to give water-absorbing composite B.

Example 3

[0120] The procedure of Example 1 was repeated except that the polyesternonwoven fabric substrate used in Example 1 was replaced by apolypropylene/polyethylene nonwoven fabric substrate (basic weight: 100g/m²) to give water-absorbing composite C.

Example 4

[0121] The procedure of Example 1 was repeated except that the polyesternonwoven fabric substrate used in Example 1 was replaced by a rayonnonwoven fabric substrate (basic weight: 50 g/m²) to givewater-absorbing composite D.

Example 5

[0122] Undried water-absorbing composite A obtained in Example 1(moisture content in the polymer 20% ) was irradiated with UV-rays at1000 mJ/cm² and then dried to a moisture content of 5% in the supportedpolymer to give water-absorbing composite E.

Example 6

[0123] The procedure of Example 1 was repeated except that the innerdiameter of nozzles for solutions A and B used in Example 1 was changedto 0.20 mm to give water-absorbing composite F.

Example 7

[0124] The procedure of Example 1 was repeated except that solution Aused in Example 1 was replaced by a solution prepared by adding 27.4parts by weight of maleic anhydride, 68.9 parts by weight of 48.5% byweight sodium hydroxide, 18.0 parts by weight of water, 0.15 parts byweight of a crosslinker (N,N′-methylenebisacrylamide) and 5.0 parts byweight of an aqueous 30% by weight hydrogen peroxide solution as anoxidizing agent to 100 parts by weight of an aqueous 80% by weightacrylic acid solution and solution B used in Example 1 was replaced by asolution prepared by adding 27.4 parts by weight of maleic anhydride,68.9 parts by weight of 48.5% by weight sodium hydroxide, 21.5 parts byweight of water, 0.15 parts by weight of a crosslinker(N,N′-methylenebisacrylamide) and 1.5 parts by weight of L-ascorbic acidas a reducing agent to 100 parts by weight of an aqueous 80% by weightacrylic acid solution to give water-absorbing composite G.

Example 8

[0125] An aqueous 5% ethylene glycol diglycidyl ether solution wassprayed with spray nozzles on water-absorbing composite A obtained inExample 1 to impregnate the polymer with the solution, and then thepolymer was dried to a moisture content of 5% in the polymer to givewater-absorbing composite H.

Example 9

[0126] The procedure of Example 1 was repeated except that the supportedpolymer content in Example 1 was changed to 100 g/m² to givewater-absorbing composite I.

Comparative example 1

[0127] Solutions A and B prepared in Example 1 were warmed to 40° C. andpumped at a flow rate of 5 m/sec using nozzles having an inner diameterof 0.13 mm.

[0128] Solution A formed liquid columns from nozzle tips and then becamedroplets to fall in a gas phase (in the air at a temperature of 50° C.).These droplets were received on a polyester nonwoven fabric substrate(basic weight: 30 g/m²) placed 3 m below nozzles tips, and solution Bprepared in Example 1 was sprayed in the same manner as for solution A.

[0129] Solutions A and B reacted with each other to advancepolymerization, thus forming a water-absorbing polymer. This was driedto a moisture content of 5% to give water-absorbing composite J having asupported polymer content of 200 g/m².

[0130] A light microphotograph of this water-absorbing composite J isshown in FIG. 5 using a scale of 1.5 mm.

Comparative Example 2

[0131] The procedure of Example 1 was repeated except that the polyesternonwoven fabric substrate used in Example 1 was placed 20 cm belownozzle tips, with the result that polymerization proceeded on thesubstrate to give water-absorbing composite L without formingagglomerates.

Comparative Example 3

[0132] The procedure of Example 1 was repeated except that the polyesternonwoven fabric substrate used in Example 1 was placed 5 m below nozzletips to give water-absorbing composite M comprising almost completelypolymerized agglomerates deposited on the substrate.

Comparative Example 4

[0133] Water-absorbing composite N was obtained by the process describedin Example 1 of JP-A 67403/97.

[0134] A scanning electron microphotograph of this water-absorbingcomposite N is shown in FIG. 6 using a scale of 500 μm.

Comparative Example 5

[0135] Water-absorbing composite P was obtained by the process describedin Example 1 of JP-A 239912/97.

Test Examples

[0136] Each water-absorbing composite obtained in Examples 1-9 andComparative examples 1-5 was measured and tested as follows.

[0137] (1) Proportion of the Polymer in the Form of Agglomerates

[0138] On scanning electron microphotographs (SEM photographs) of pluralsites of each water-absorbing composite, 100 particles were randomlyselected to determine whether or not they form agglomerates. Theproportion of the polymer in the form of agglomerates was calculatedsupposing that the density of agglomerates is homogeneous.

[0139] (2) Average Particle Diameter of Agglomerates

[0140] On SEM photographs of plural sites of each water-absorbingcomposite, 100 particles were randomly selected to measure theirparticle diameters, from which the average was calculated.

[0141] (3) Residual Unreacted Polymerizable Monomer Level

[0142] Precisely weighed 0.5 g of each water-absorbing composite wassufficiently swollen with 1 liter of ion-exchanged water in a 2-literbeaker with stirring for about 10 hours. The swollen polymer gel wasfiltered off through a 200-mesh sieve and the filtrate was analyzed byhigh-speed liquid chromatography. Separately, a monomer standardsolution showing a known concentration was prepared to derive acalibration curve representing an absolute concentration scale.

[0143] (4) Supporting Strength of Water-Absorbing Polymer to FibrousSubstrate

[0144] A sheet-like sample of 60 mm×300 mm (thickness: 0.5-20 mm) ofeach water-absorbing composite was absorbed with physiological saline tosaturation and then placed on a stone table, and a roller having adiameter of 105 mm, a width of 60 mm and a weight of 4 kg was run on thesample to measure the dried weight of the water-absorbing polymerseparated from the sample during 5 reciprocations at a speed of 10cm/sec and to evaluate supporting percentage A represented by theequation below. The supporting percentage is preferably 60% or more forproviding practically acceptable supporting strength, and morepreferably 70% or more.

A(%)=[(W0−w)/W0]×100

[0145] where W0 represents the dried weight of the water-absorbingpolymer in the sample and w represents the dried weight of the separatedwater-absorbing polymer.

[0146] (5) Physiological Saline-Absorbing Capacity

[0147] In a 300 ml beaker were weighed about 1.0 g of eachwater-absorbing composite and about 200 g of 0.9% physiological salineand allowed to stand for about 4 hours to sufficiently swell the polymerwith physiological saline. After drainage through a 100-mesh sieve,physiological saline-absorbing capacity B was calculated according tothe equation below to evaluate water-absorbing capacity of the supportedwater-absorbing polymer.

B=(W1−W2)/W3

[0148] where W1 represents the weight of the water-absorbing compositeafter absorbing water, W2 represents the weight of the substrate aloneafter absorbing water, and W3 represents the weight of thewater-absorbing polymer supported on the water-absorbing composite.

[0149] (6) Water-Absorbing Speed

[0150] In a 300 ml beaker were weighed about 1.0 g of eachwater-absorbing composite and about 200 g of 0.9% physiological salineand allowed to stand for 5 minutes to sufficiently swell the polymerwith physiological saline. After drainage through a 100-mesh sieve,physiological saline-absorbing capacity B was calculated according tothe equation above to evaluate water-absorbing speed of the supportedwater-absorbing polymer.

[0151] (7) Polymerization Degree During Falling on the Substrate

[0152] Polymerization was initiated to form droplets of the reactionmixture in a gas phase and the resulting agglomerates underpolymerization were fallen in a beaker containing is methanol weighed tohave a liquid level in flush with the substrate. The monomer weight inmethanol was determined by liquid chromatography. The polymer inmethanol was dried under reduced pressure at 130° C. for 3 hours, andthen the weight was determined. The polymerization degree was calculatedfrom both weights according to the equation below.

Polymerization degree=Mp/(Mm+Mp)×100

[0153] where Mp represents the polymer weight and Mm represents themonomer weight.

[0154] (8) Frequency Intensity Ratio

[0155] Agglomerates were photographed at a magnification of 160x or 300xusing a scanning electron microscope (Hitachi S2400). Particle contourson these photographs were faithfully traced with a mechanical pencil(HB, 0.5 mm φ) on a tracing paper and the traced image was reduced to ahalf for image analysis. The image was scanned with a scanner (CanonCanoScan 300) at a resolution of 75 dpi. The resolution of measurablelength in the scanned image was 2.3 μm (80x) or 1.25 μm (150x). Thescanned contour image was converted into text file after the inside ofthe contour image was painted out (using a commercially availablesoftware such as Adobe Photoshop and NIH image, for example).

[0156] The painted figure including the contour was expressed as abinary pattern (0,1) to find the center of gravity (Gx, y). If all thefour pixels on four sides surrounding a target black pixel are “1”, thetarget pixel was judged as an inner pixel to determine the contour (aclosed curve of the boundary of the figure). Then, black pixels formingthe contour were continuously traced to derive the coordinate sequence(Yi, Xi) of the contour line consisting of m data.

[0157] The distances between the center of gravity and pixels formingthe contour line were determined for the whole coordinate sequence ofthe contour line, and then the distances from the center of gravity werenormalized by dividing each distance from the center of gravity by theaverage distance and subtracting “1” to give a normalized distance.

[0158] Normalized distance=(Distance from center of gravity/averagedistance)−1

[0159] Before frequency analysis of the normalized distances, the numberof data varying with particles was normalized to 512. In order toconvert m data of normalized distances into 512 data, 2 data flanking atarget datum were used for interpolation.

[0160] The normalized distance consisting of a sequence of 512 data wasFourier-transformed to derive a power spectrum. The power spectrum wasintegrated from low to high frequency sides to give the integral of thepower spectrum.

[0161] To define features of the figure, the ratio between the integralat frequency 5 (Ipw, 5) and the integral at frequency 20 (Ipw, 20) ofthe power spectrum was determined as frequency intensity ratio. Thefrequency intensity ratio is greater for ellipses or similar figures(containing much low-frequency components), but smaller for figures withcomplex contour lines (containing much high-frequency components).

Frequency intensity ratio=(Ipw, 5)/(Ipw, 20).

[0162] (9) Average Relative Displacement of the Direction

[0163] A relative displacement of the direction (Δθ) was calculated fromthe coordinate sequence (Yi, Xi) of the contour line. The relativedisplacement of the direction is defined by the equation below. That is,the relative displacement of the direction of an i-th contour datum(Δθi) is a directional difference between a vector joining the i-thdatum (Xi, Yi) to a (i+n)-th datum (Xi+n, Yi+n) and a vector joining a(i−n)-th datum (Xi−n, Yi−n) to the i-th datum (Xi, Yi) and the relativedisplacement of the direction is 0° if both vectors have the samedirection. There is no discrimination between right and left directionsof variation.

Δθi=(tan⁻¹(Yi+n−Yi)/(Xi+n−Xi)-tan⁻¹(Yi−Yi−n)/(Xi−Xi−n))×180/π

[0164] where n=5 in view of the minimum variation angle of 45° (π/4radian), which causes too large stepping pitch to increase the influenceof digitization error if n=1. The relative displacement of the directionwas calculated according to the equation below.

[0165] Average relative displacement of the direction(θ)=(Δθi−360xn)/number of data (m)

[0166] where the correction term “360xn” was introduced because the sumof relative displacement of the direction is 360° even for a circle. nwas introduced because the sum of all the data means the sum of nrelative displacement direction.

[0167] The average relative displacement of the direction is a valuedefining complexity of a particle contour line and it is greater forcomplex shapes having a more irregular contour.

[0168] Calculations were made considering that coordinate sequences (X1,Y1) and (Xm, Ym) are continuous because coordinate data in these dataprocesses are characterized by a closed curve of a contour line. Theaverage of randomly sampled three or more particles was used fordigitization.

[0169] (10) The Maximum Length/Minimum Length Ratio

[0170] The maximum and minimum length of agglomerates were determinedfrom processed images of agglomerates. As used herein, the maximum andminimum length refer to the maximum and minimum lengths as diameters ofagglomerates but may not be necessarily orthogonal. The maximumlength/minimum length ratio was calculated by dividing the maximumlength by the minimum length. Any material having a maximumlength/minimum length ratio less than 1.2 cannot be considered as anagglomerate structure.

[0171] These measurements and test results are summarized in the tablebelow. TABLE 1 Example/Comparative example Examples Comparative Examples1 2 3 4 5 6 7 8 9 1 2 3 4 5 Water-absorbing A B C D E F G H I J L M N Pcomposite Proportion of the polymer 85 80 85 83 86 79 75 86 72 3 8 68 095 in the form of agglomerates (%) Average particle 550 600 500 520 530750 460 550 460 little little 450 200 500 diameter of grains grainsagglomerates (μm) Physiological saline- 40 35 37 41 38 34 30 37 43 20 2244 35 35 absorbing capacity (g/g) Water-absorbing speed 30 27 36 29 3225 20 32 34 10 11 35 23 25 (g/g) Residual unreacted 150 170 140 160 60180 190 130 180 2000 350 90 200 200 polymerizable monomer level (ppm)Supporting strength of 80 78 75 83 83 82 74 82 84 92 87 15 85 94water-absorbing polymer to fibrous substrate (%) Polymerization degree82 90 82 82 82 75 60 82 82 0 0 99 15 — during falling on the substrate(%) Frequency intensity ratio 0.75 0.69 0.73 0.74 0.73 0.62 0.8 0.740.77 0.7 0.68 0.88 0.74 0.58 Average relative 18 14 19 20 18 21 13 21 164 6 9 8 11 displacement of the direction by direction analysis Aspectratio 1.8 1.8 1.3 1.8 1.7 1.5 1.3 1.6 1.3 1.1 1.1 1.2 1.2 1.3

Example 10

[0172] Solution A was prepared by adding 9 parts by weight of an aqueous30% by weight hydrogen peroxide solution to 237.4 parts by weight of apartially neutralized aqueous acrylic acid solution (monomer content 50%by weight) containing N,N′-methylenebisacrylamide at 0.07 mol % on thebasis of (preneutralized) acrylic acid in acrylic acid neutralized to60% with sodium hydroxide. Solution B was prepared by adding 1.0 part byweight of L-ascorbic acid to 237.4 parts by weight of the same aqueousacrylic acid solution. The prepared solutions A and B were flown out ata rate of 5 m/sec from their respective nozzles (inner diameter 0.1 mm)provided at the ceiling of a polymerization chamber containing apolyester nonwoven cloth (fiber diameter 25-30 μm, basic weight 35 g/m²)on the floor level and opposed to each other at a height of 3 m abovethe floor level. Both solutions were collided in the air to formdroplets, which were fallen on the nonwoven cloth forming a fibroussubstrate as they were polymerized in an atmosphere at 40-50° C. Then,the nonwoven cloth on which incompletely polymerized particles weredeposited was removed from the polymerization chamber and heated tocomplete polymerization into water-absorbing composite Q. The resultingwater-absorbing composite Q had a water-absorbing polymer particlecontent of 200 g/m². Polymer particles had a primary particle diameterof 100-600 μm and agglomerates of primary particles had a particlediameter of 300-3000 μm. The proportion of agglomerates was about 90% ormore.

[0173] Thus prepared water-absorbing composite Q and water-absorbingcomposite N prepared in Comparative example 4 were used as absorbentmaterials to prepare 6 types of water-absorbing articles (diapers)having a structure as defined in Table 2 selected from FIG. 7(a)-(e).The articles were prepared to have a water-absorbing face at the top onthe figure. Each structure contains a polyethylene film 16 (basic weight20 g/m²), a fluffy pulp layer 13 (basic weight 110.5 g/m²), awater-absorbing material having water-absorbing polymer particles 15immobilized on a fibrous substrate 14, a tissue paper 12 (basic weight18 g/m²) and a polyester fiber nonwoven cloth 11 (basic weight 30 g/m²).However, the structure of FIG. 7(e) uses a pulp mix havingwater-absorbing polymer particles uniformly dispersed in fluffy pulp inplace of the water-absorbing material having water-absorbing polymerparticles bonded to one side of a fibrous substrate. The pulp mix wasprepared by combining water-absorbing polymer particles obtained asabove but not adhered to the nonwoven cloth and said fluffy pulp at awater-absorbing polymer content of 200 g/m² and a pulp content of 256g/m².

[0174] Each diaper prepared was tested for the speed of absorbingartificial urine and the amount of artificial urine released as follows.An acrylic plate (100×100×10 mm, overall weight 150 g) equipped at thecenter with a cylinder of 40 mm in inner diameter opened at the top andhaving 7 penetrations of 5 mm in diameter almost evenly spaced insidethe circle surrounded by the cylinder was mounted at the center of eachdiaper prepared (180×180 mm), and a disk (500 g) of 100 mm in diameterhaving a hole of 45 mm in diameter at the center was further mountedthrough the cylinder. Artificial urine (25 ml) was introduced into thecylinder to measure the time with a stopwatch until it is absorbed.After 10 minutes, the disk and acrylic plate were removed and 20 pliesof filter paper (ADVANTEC No. 424, 100×100 mm, Toyo Roshi) were mountedat the same position as that of the acrylic plate on the diaper and aweight of 4 kg was further mounted on the filter paper. After 5 minutes,the weight was removed and the weight of the filter paper was measuredto determine the amount of artificial urine absorbed to the filterpaper. This measurement was repeated three times. The results are shownin the table below, in which the water-absorbing speed is expressed inseconds and the released amount is expressed in g. TABLE 2 First testSecond test Third test Total Water- Water- Water- Water- Water-absorbing absorbing Released absorbing Released absorbing Releasedabsorbing Released Sample composite Structure speed amount speed amountspeed amount speed amount 1 Q a 5.7 2.0 80.0 4.5 122.6 6.9 208.3 13.4 2Q b 4.8 5.0 12.2 5.0 22.9 6.0 39.9 16.0 3 Q c 4.2 1.9 7.1 1.9 8.8 4.120.1 7.9 4 Q d 5.3 10.3 11.8 9.8 18.5 10.7 35.6 30.8 5 Q e 6.0 0.2 38.14.8 56.0 12.7 100.1 17.7 6 N c 4.9 1.2 10.3 4.9 14.0 7.1 29.2 13.2

[0175] When comparing the results of samples 1 and 2, the diaper ofsample 1 having a water-absorbing face on the water-absorbing resinparticle side shows much lower water-absorbing speeds in the second andthird tests as compared with the diaper of sample 2 having awater-absorbing face on the fibrous substrate side according to thepresent invention. Among diapers of the present invention, sample 3having a fluffy pulp layer on the water-absorbing resin particle side issuperior to sample 4 having a fluffy pulp layer on the fibrous substrateside in both absorbing speed and released amount. Sample 5 is aconventional diaper, which shows lower water-absorbing speeds in thesecond and third tests.

[0176] The diapers of sample 2 and sample 5 prepared as above weretested for the transfer amount of water-absorbing resin particles in thediapers when a force rubbing the diapers was repeatedly applied. Eachdiaper of 180×180 mm having absorbed water in an amount 50 times theweight of the water-absorbing resin was mounted on a shaking table, andan acrylic plate of 120×120 mm curved in a semicircle was furthermounted thereon so that the outer center of the semicircle coincideswith the center of the diaper. The inner center of the semicircle has aninsertion part, in which the post of a T-shaped weight (3 kg) wasloosely inserted while it was supported at the center of a plate of100×100 mm. When the shaking table oscillates, the weight swings aroundthe post so that the acrylic plate reciprocates to rub the diaper. Afterthe shaking table was oscillated for 5 minutes at 80 reciprocations/min,the center of the diaper was cut out into a size of 100×100 mm todetermine the reduction percentage of water-absorbing resin particles.The results showed that the reduction percentage of the water-absorbingresin of the diaper of sample 2 was 15% in contrast to the diaper ofsample 5 in which the reduction was 29% , i.e. almost doubled.

[0177] In water-absorbing composites of the present invention, most ofthe highly water-absorbing polymer forms proper agglomerates stablyimmobilized on a fibrous substrate. They exhibit excellentwater-absorbing properties, a high water-absorbing speed and anexcellent immobility of swollen gel after absorbing water. According toprocesses of the present invention, water-absorbing compositesexhibiting excellent performance can be simply and economically preparedwith little residual monomer content. Therefore, water-absorbingarticles using a water-absorbing composite of the present invention or awater-absorbing composite prepared by a process of the present inventionare of very high practical value and utility.

[0178] Having described the present invention, it will now be apparentto one of ordinary skill in the art that many changes and modificationsmay be made without departing from the spirit and the scope of thepresent invention.

1-23 (canceled)
 24. A process for preparing a water-absorbing composite,comprising; a) forming droplets of a reaction mixture initiated bymixing a) an aqueous solution of a polymerizable monomer giving awater-absorbing polymer with b) a redox polymerization initiator in agas phase; b) combining said droplets into agglomerates while nearlymaintaining their primary particle shapes in the gas phase or on afibrous substrate, or both; c) supporting said agglomerates formed inthe gas phase on said fibrous substrate; and then d) completingpolymerization of said agglomerates on said fibrous substrate toimmobilize said agglomerates on said fibrous substrate.
 25. The processof claim 24, wherein said polymerizable monomer has a polymerizationdegree of about 20-97% when it comes into contact with said fibroussubstrate.
 26. The process of claim 24, wherein said droplets of saidreaction mixture are formed by mixing a first solution containing anoxidizing agent forming the redox polymerization initiator and theaqueous polymerizable monomer solution and a second solution containinga reducing agent forming the redox polymerization initiator and theaqueous polymerizable monomer solution in a gas phase.
 27. The processof claim 26, wherein said mixing is performed by colliding said firstsolution and said second solution in a liquid column state.
 28. Theprocess of claim 24, wherein said polymerizable monomer is based on analiphatic unsaturated carboxylic acid or a salt thereof.
 29. The processof claim 24, wherein said polymerizable monomer is based on acrylic acidin which 20 mol % or more of the carboxyl group is neutralized into analkali metal salt or an ammonium salt.
 30. The process of claim 24,wherein the oxidizing agent forming said redox polymerization initiatoris hydrogen peroxide and the reducing agent is L-ascorbic acid or anL-ascorbic acid alkali metal salt.
 31. The process of claim 24, whereinsaid fibrous substrate comprises synthetic fibers, natural fibers, orsemisynthetic fibers. 32-51 (Canceled)